This invention relates to apparatuses for separating and recovering liquid or solid particles suspended in a forced gas flow.
The separation and recovery of liquids or solids suspended in a gas flow is often required in air knife coating devices, sand blasting devices, etc. In the air knife coating method, the surface of a continuously running web of metal or some other material is coated with coating material or the like by an applicator roll or a liquid injector, and the excess coating is thereafter removed by an air jet blown against the web surface to thereby control the coating thickness and smooth the web surface. Accordingly, it is necessary to separate the removed coating material from the air flow and recover it for reuse.
In sand blasting, an abrasive such as sand is blown under pressure against the surface of a web such as a plastic film, a metal plate or the like to abraid, polish or matt the surface, whereby it is similarly necessary to separate and recover the abrasive.
Recovery apparatuses for air knife or sand blast coating devices are disclosed in U.S. Pat. Nos. 3,229,447, 3,397,673 and 3,550,553, and in Japanese Patent Application Publication No. 33023/1971. A typical one is shown in FIG. 1, wherein a coating roll 2 picks up coating material 4 from a pan 3 and applies it to a continuously running web 1. The amount of coating material applied to the web exceeds a predetermined value. While the coated web is supported by a backing roll 5, an air jet from a slit-shaped nozzle 7 of an air doctor 6 is blown against the web surface to remove excess coating material therefrom so that the remaining amount of coating material reaches the predetermined value. A mixture 8 of air and removed coating material is deflected by a separating plate 9 and flows along a guide board 10 disposed below the separating plate. The direction of the air mixture flow is changed at the end of the guide board, whereby the heavier than air coating material is separated from the air flow and collected in a first chamber 11. The air mixture flow containing some residual coating material is then directed along an opposite wall 12 of the recovery apparatus to undergo a further change of direction, whereby the residual coating material is collected in a second chamber 13 and the air is thereafter discharged from the system.
When the air mixture strikes the plate 9 some coating material is separated from the air, but since the flow path is directed along the guide board 10 without collecting the separated coating material, it is facilitated that some of such separated coating material is reentrained, thereby lowering the efficiency of the apparatus. Furthermore, the air flows back across the separated coating material which drops of the end of the guide board 10 to thereby reentrain some of such coating material and further reduce the efficiency of the apparatus.
To avoid such difficulties an improved recovery apparatus was developed, as disclosed in Laid-Open Japanese Patent Application No. 21423/1974. In this apparatus, as shown in FIG. 2, a first chamber 11 is provided just below the end of a separating plate 9 to immediately collect the coating material 4 which has been initially separated from the air mixture. The air mixture containing residual coating material thereafter strikes the wall 12 of the recovery apparatus opposite the separating plate 9, and flows along such wall. The coating material separated during this period is collected in a second chamber 13. The air mixture continues past the chamber 13 along the prolongation line of the wall such that its direction is changed, as a result of which any remaining coating material is collected in a third chamber 14 while the air is discharged through a duct 15. In this apparatus the separated coating material falling from the end of the plate 9 is not disturbed by any cross-flow of the mixture 8, thereby more effectively maintaining the separation.
In this apparatus, however, the air mixture flowing along the separating plate 9 strikes against the apparatus wall confronting the plate and thereafter follows along the wall. Accordingly, the partially separated coating material is scattered or reentrained in the air flow as a result of such striking, which decreases the separation efficiency. Further, some of the energy provided by the air doctor is lost because of the striking, whereby the centrifugal separating force cannot be as effectively utilized. Furthermore, because of the unsmooth air flow the pressure loss is sometimes increased, or some air having coating material entrained therein is wastefully discharged outside the apparatus, which leads to air pollution.